Carb jetting - Need help interpreting manual

[connor1]

The tech section references an online how to "http://www.iwt.com.au/mikunicarb.htm" as a good guide to understand how to tune the Mikuni carbs. I have a 72 XS aafter warm up, my midrange performance sucks. The engine seems to stumble all over itself. I am thinking about pulling the carbs, taking them apart and cleaning and adjusting them. However, I cannot make out what the author is talking about in the sentances below in regard to jetting under fig 7.




"While jetting carburetors, place a piece of tape on the throttle housing. Place another piece of tape on the throttle grip and draw a line (while the throttle is at idle) straight across from one piece of tape to the other. When these two lines are lined up, the engine will be idling. Now open the throttle to full throttle and draw another line directly across from it on the throttle housing. At this point, there should be two lines on the throttle housing, and one on the throttle grip."


If I draw a line from the grip to the throttle housing it will not be straight as it will have to go down my handlebars, across the gas tank, on to the head and finally to the carb where I believe the throttle, and therefore the throttle housing is located.

Maybe I dont understand what the throttle housing is? Is the author referring to the switch housing that is mounted on the handlebars adjacent to the throttle grip? Is this where the second piece of tape goes for reference later?

 

[weekendrider]

Well if you are trying to judge how much throttle you are using(1/4-1/2-3/4) it would be tape on the grip and tape on the housing for your kill switch, starter button.

If on the carb it might be the part that holds the cable and the carb body the throttle rod turns in/goes through both down on the carbs.

I'm too lazy to look at the link so going out on a limb I'm saying they are wanting you to
degree the travel of the throttle so you will have idea of where half and three quarter turns are. Throttle chops?

 

[connor1]

The more I think about it, the author MUST be referring to the starter switch housing....unless I am missing something, that seems to makes sense as a reference for throttle position.

 

[weekendrider]

Yes if indexing the throttle twist.

 

[5twins]

Yes, he is referring to indexing the twist grip to the housing it turns in but ..... that really doesn't help much when tuning CV type carbs like we have. It's more for a regular slide type carb. Watch your RPMs instead.

Yes, clean your carbs. Pretty much all these bikes need that done when you get one. Your needle jets and the area around them (the bored hole they fit into) may be all gummed up.

 

[XSLeo]

The throttle housing is the housing that holds the throttle grip. On some bikes that's all it does, others it holds some switches.
These marks can help determine throttle position. You can use this info to help tune the carbs.
Leo